This invention relates generally to voltage reference circuits and in particular to a support circuit for supporting various types of voltage reference circuits including bandgap reference circuits, zener reference circuits, and reference amplifier circuits.
Voltage reference circuits provide a reference voltage that is independent of temperature and supply voltage variations. The reference voltage is provided to other circuits that depend on a known, stable voltage to operate properly, including for example analog to digital converters (ADCs), digital to analog converters (DACs), filters, and other analog integrated circuits.
Various circuit topologies exist for voltage reference circuits including bandgap reference circuits, zener reference circuits, and reference amplifier circuits. Bandgap reference circuits are well known in the art for generating reference voltages by balancing the temperature coefficients of multiple semiconductor diode and transistor junctions. Zener reference circuits employ the precise junction voltage settings of a reference zener which is commonly understood to be a combination of forward-biased zener diode and a silicon diode. The reference zener is biased with a known bias current. Reference amplifier circuits use the voltage settings of the base emitter voltage across a transistor which is operated at a specific collector current in conjunction with a zener diode biased at specific zener current to achieve substantially a zero temperature coefficient output voltage.
Each of the types of voltage reference circuits require additional support circuitry around them in the form of output buffers, amplifiers, or dividers to obtain the desired reference voltage. Furthermore, if both negative and positive reference voltages are required, additional inverting buffers are required. A voltage or current regulator is typically supplied in order to deliver a more stable supply voltage or bias current to the voltage reference circuit in order to improve its stability. Such support circuits typically have been implemented as specific designs for each particular application and have been re-designed for each new application.
Furthermore, most voltage reference circuit designs involve circuits that are implemented on an integrated circuit level, taking advantage of the complementary negative and positive temperature coefficients of various semiconductor junctions on the same substrate. Such designs allow for generally good performance in obtaining a reference voltage in one polarity but provide no provision for easily generating the reference voltage in the opposite polarity in a manner that allows for amplitude tracking between the positive and negative voltages.
Therefore, it would be desirable to provide a reference voltage support circuit that may accommodate a variety of voltage references, including bandgap reference circuits, zener reference circuits, and reference amplifier circuits. The reference voltage support circuit provides a stabilized supply current to the voltage reference and generates both negative and positive reference voltages from the voltage reference circuit. It would be further desirable that the amplitudes of the negative and positive reference voltages track each other closely over time and temperature with a minimal amount of additional circuitry.